1. Field of the Invention
The present invention relates to an impeller arranged to generate an air stream flowing along a center axis and more specifically, to a blower fan using such an impeller.
2. Description of the Related Art
In a conventional impeller for use in a blower fan, a plurality of blades fixed to the outer circumferential surface of a cylindrical impeller cup rotates about a center axis to thereby generate an air stream flowing along the center axis.
During rotation of the impeller, radial centrifugal forces act on the blades. The influence of the radial centrifugal forces become more significant as the rotation speed of the impeller becomes greater. In case of a blade with an increased swept-forward degree, the radial outer end of the blade is positioned more forward in the rotational direction than the base thereof. For that reason, an increased moment is generated in the base due to the radial centrifugal forces acting on the respective portions of the blade. Thus, there exists a demand that the impeller be designed to sufficiently bear the radial centrifugal forces.
U.S. Patent Application Publication No. 2008/0056899 discloses a technique in which the strength of blades is increased by interconnecting the blades with a ring-shaped connector portion to reduce the influence of radial centrifugal forces.
In the disclosure of the reference cited above, however, no consideration is given to the impeller characteristics affected by the interference between the air streams generated by rotation of the blades and the ring-shaped connector portion. This interference between the air streams generated by rotation of the blades and the ring-shaped connector portion may deteriorate the impeller characteristics.